<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <link rel="stylesheet" href="test.css"/>
    <style>
        #test{
        width: 200px;height: 200px;background-color: #002d32;
            position: absolute;
            top: 300px;
            left: 20px;
        }
    </style>
</head>
<body>
<div id="test">2222222222</div>

<script>

    var a;
    // a 的值是 undefined
    console.log("The value of a is " + a);

    // Uncaught ReferenceError: b is not defined
//    console.log("The value of b is " + b);

    // c 的值是 undefined
    console.log("The value of c is " + c);
    var c;

    // Uncaught ReferenceError: x is not defined
    console.log("The value of x is " + x);
    let x;
</script>
</body>
</html>
